This invention relates to a process for production of higher alkanes, and particularly for production of the C7 hydrocarbons 2,2,3-trimethylbutane (also known as “triptane”) and 2,2,3-trimethylbut-1-ene (also known as “triptene”) by homologation of dimethyl either and/or methanol, in a feed containing the same. Collectively, these two compounds will be referred to herein as “triptyls”. In general, processes that produce triptane may also produce triptene, which may be wholly or partly converted to triptane during the process. Both compounds have equivalently high octane numbers.
It has been known for quite some time that certain branched hydrocarbons, and triptyls in particular, provide high octane properties to fuels such as gasoline and jet fuel. U.S. Pat. No. 6,855,857 of Boesveld et al. describes a process for selectively isomerizing hydrocarbons including paraffinic hydrocarbons (both cyclic and acyclic), alkyl-substituted aromatic hydrocarbons, or mixtures of such hydrocarbons, in the presence of a Lewis acid isomerization catalyst, notably a transition metal halide or salt of fluorosulfuric, trifluoromethanesulfonic, or trifluoroacetic acid. Selectivity to triptane of from about 8 to about 16% is reported.
US published patent application 2004/249228 of Boesveld et al. describes a process for producing triptane from a mixed fed containing both cyclic and acyclic hydrocarbons, with preferably at least 30% of the feed being acyclic hydrocarbons, and preferably primarily C7 hydrocarbons, using a combination catalyst having both a metal function and an acidic function. The acidic function is preferably provided by a zeolite, preferably a faujasite-type zeolite such as ECR-30, ECR-32, ZSM-5, ZSM-3 or ZSM-20. U.S. Pat. No. 4,508,618 of Olah et al. describes a process for increasing the octane number of natural gasoline using a trifluoromethanesulfonic acid catalyst. However, very little triptane was produced in the sole example in that patent.
Technologies for producing gasoline fractions, including triptane, from dimethyl ether and/or methanol, have been investigated for a good number of years. For example, U.S. Pat. Nos. 4,059,646 (Wald et al.), 4,059,647 (Wald et al.), 4,126,642 (Kim et al.), 4,151,214 (Wald et al.) 4,166,189 (Wald et al.), and 4,209,031 (Drent et al.), and US published application 2004/133055 (Cook et al.) describe processes for production of triptane from dimethyl ether and/or methanol using various zinc halide catalysts. US published application 2007/004955 (Kay et al.) describes a process for producing triptane from dimethyl ether and/or methanol using an indium halide catalyst. However, halide catalysts and other halide-containing materials have the disadvantage of introducing metallurgical complexity in the overall process due to corrosion and the leaching of halides as part of the products stream.
Previous work by researchers at Mobil Oil Company describe production of gasoline and of light olefins from dimethyl ether and/or methanol (“MTG” or “methanol-to-gasoline” and “MTO” or “methanol-to-olefins” processes, respectively) using various acidic zeolites. Temperatures were approximately 573K, and there was little selectivity to triptane.
It would be desirable to possess a process for production, especially selective production, of triptane from dimethyl ether and/or methanol. Such a process is provided by this invention. It would be particularly useful to carry out such processes with reactants and most products in the gas phase and without the use of halides.